The conventional wisdom has been that polar bears don't eat on land or do much at all except snooze and conserve their energy before the bay refreezes.

But as the climate warms, the sea ice doesn't last as long. Already the bears are showing up on land, on average, three weeks earlier than in the 1980s, according to Gormezano. And by the late 2060s, the western Hudson Bay could be ice free for up to six months.

Turf, Not Surf

In 2010 an analysis of the bears' energy needs by ecologist Peter Molnar—now at Princeton University—and his colleagues suggested that six months without food would kill 28 to 48 percent of adult male polar bears. At that rate, the population would likely crash.

But this analysis assumed that bears don't eat anything on land. Gormezano said this isn't true.

An adult male in bad condition would need the full menu of tundra foods listed above to make it through the ice-free months. Gormezano's analysis considered adult males, as did Molnar's, because the math is more straightforward without factoring in the demands of growth or reproduction.

But her observations show that typically females and cubs chase geese and gnaw on caribou.

Polar Bear Decline

An unanswered question is whether the energetic cost of chasing after a goose or a caribou is worth the calories the food supplies. If so, there are lots and lots of geese and, these days at least, plenty of caribou in the Hudson Bay area, Gormezano said.

"There is potential for this to prevent starvation under the scenarios that Molnar put out there," she said. "However, it does depend on how much energy they spend getting this food." (See more polar bear pictures.)

Molnar hasn't looked at the analysis in depth, but he's skeptical, given trends in this population of polar bears.

"The population has declined quite substantially between 1995 and 2005," he said.

"We know that their body conditions are getting worse. They are getting thinner. The real question is not, Can you put land-based feeding into the models or not? The real question is, Why aren't the bears eating enough to prevent declines?"